1. Field of the Invention
The present invention relates to a deposit measurement apparatus, a deposit measurement method, and a computer-readable storage medium storing a deposit measurement program that estimate the blockage ratio or the thickness of deposited scale due to scale deposits at a gap between a wall surface of a through-hole and an outer surface of a heat-conducting pipe in a heat exchanger of a steam generator etc., provided with a pipe-supporting plate in which the through-hole for inserting the heat-conducting pipe is formed.
This application is based on Japanese Patent Application No. 2011-001269, the contents of which are incorporated herein by reference.
2. Description of Related Art
For a steam generator, etc. in a pressurized water reactor plant, there is a known method of estimating the amount of iron (II, III) oxide scale deposited on an outer surface of a heat-conducting pipe on the basis of eddy-current flaw detection signals. Particularly in the case in which a pipe hole in a pipe-supporting plate is irregularly shaped, there is a known method of estimating the proportion by which the gap between the heat-conducting pipe and the pipe-supporting plate is blocked by scale (blockage ratio) on the basis of eddy-current flaw detection signals.
As a method of calculating the above-described blockage ratio, there is a generally known method in which a bobbin-coil eddy-current flaw detection probe is employed. In this method, an amplitude in a specific direction is measured based on eddy-current flaw detection signals detected by the bobbin-coil eddy-current flaw detection probe, and a blockage ratio that corresponds to the measured amplitude is obtained from a calibration curve.
Because an eddy current flows in the entire circumferential direction in the bobbin-coil probe described above, for example, it is not possible to separate signals originating from scale at a pipe-supporting-plate gap (a portion where the outer surface of the heat-conducting pipe and the inner surface of the pipe-supporting plate are separated) and signals originating from the pipe-supporting plate. Accordingly, due to differences in positions where the scale is deposited, etc., the waveforms of the eddy-current flaw detection signals become variable even if the blockage ratios are the same; therefore, the precision in estimating the blockage ratio is low.
In order to solve the problem arising from combining the pipe-supporting-plate signals described above, Japanese Unexamined Patent Application, Publication No. 2002-181793 proposes a technique in which an eddy-current flaw detection signal is obtained as a basic signal when there are no deposits; a Lissajous waveform for a deposit signal is obtained by subtracting the basic signal from an eddy-current flaw detection signal for a subject pipe on which deposits collected in an actual apparatus are deposited; and a blockage ratio corresponding to the amplitude thereof is determined from a calibration curve.